Sen. Ted Cruz has vowed to support GOP front-runner Donald Trump if he secures the Republican nomination -- but he has one condition.

"I can give you one example where I would no longer support Donald Trump. If for example, he were to go out on Fifth Avenue and shoot somebody, I would not be willing to support Donald Trump," Cruz said today at a press conference in Rockford, Illinois.

"I could stand in the middle of Fifth Avenue and shoot somebody, and I wouldn't lose any voters, okay?" Trump said, while putting his fingers into the shape of a gun and acting out pulling the trigger.

When pressed further by reporters, Cruz argued that he is a man who keeps his word.

"I know it is a shocking concept to members of the media. A shocking concept that an elected official actually does what he said. At the outset of this campaign, I committed I will support the Republican nominee. I honor my word," Cruz said.

When asked at the Republican debate last week, Cruz said he would support Trump as the nominee: "Yes. Because I gave my word that I would."

In answering a question of whether he’d support Trump as the nominee, Marco Rubio said on Saturday during a press conference in Largo, Florida, “I intend to support the Republican nominee. But it's getting harder every day."

On “This Week” with ABC’s George Stephanopoulos, Ohio Gov. John Kasich refused to say whether Trump is fit for office and made a similar argument to Rubio, saying, "Sometimes it’s really tough. I hope to be able to support whoever the nominee is."

"You’re not going to get me to answer a yes-or-no question," Kasich said Sunday. "I hope he’s going to change his rhetoric and bring people together."